The use of plastics-based composite materials when building ships of considerable size and characteristics, such as 30 to 100 meters long, has been limited heretofore by technical and economical factors that have prevented a larger use of said materials. This is due mainly to the fact that, usually, the builders have endeavored to reproduce by said materials structural shapes which were suitable for wood, steel or light alloys. The main disadvantages of these constructional principles followed heretofore were the poor stiffness of hulls at a parity of weight, due to the low modulus of elasticity of said materials, and the high building costs due to the extensive use of labor as a result of the complicated structure designed according to said principles followed until now.